package com.dslplatform.json;

import java.util.Arrays;

/** A very fast and memory efficient class to encode and decode to and from BASE64 in full accordance
 * with RFC 2045.<br><br>
 * On Windows XP sp1 with 1.4.2_04 and later ;), this encoder and decoder is about 10 times faster
 * on small arrays (10 - 1000 bytes) and 2-3 times as fast on larger arrays (10000 - 1000000 bytes)
 * compared to <code>sun.misc.Encoder()/Decoder()</code>.<br><br>
 *
 * On byte arrays the encoder is about 20% faster than Jakarta Commons Base64 Codec for encode and
 * about 50% faster for decoding large arrays. This implementation is about twice as fast on very small
 * arrays (&lt 30 bytes). If source/destination is a <code>String</code> this
 * version is about three times as fast due to the fact that the Commons Codec result has to be recoded
 * to a <code>String</code> from <code>byte[]</code>, which is very expensive.<br><br>
 *
 * This encode/decode algorithm doesn't create any temporary arrays as many other codecs do, it only
 * allocates the resulting array. This produces less garbage and it is possible to handle arrays twice
 * as large as algorithms that create a temporary array. (E.g. Jakarta Commons Codec). It is unknown
 * whether Sun's <code>sun.misc.Encoder()/Decoder()</code> produce temporary arrays but since performance
 * is quite low it probably does.<br><br>
 *
 * The encoder produces the same output as the Sun one except that the Sun's encoder appends
 * a trailing line separator if the last character isn't a pad. Unclear why but it only adds to the
 * length and is probably a side effect. Both are in conformance with RFC 2045 though.<br>
 * Commons codec seem to always att a trailing line separator.<br><br>
 *
 * <b>Note!</b>
 * The encode/decode method pairs (types) come in three versions with the <b>exact</b> same algorithm and
 * thus a lot of code redundancy. This is to not create any temporary arrays for transcoding to/from different
 * format types. The methods not used can simply be commented out.<br><br>
 *
 * There is also a "fast" version of all decode methods that works the same way as the normal ones, but
 * har a few demands on the decoded input. Normally though, these fast verions should be used if the source if
 * the input is known and it hasn't bee tampered with.<br><br>
 *
 * If you find the code useful or you find a bug, please send me a note at base64 @ miginfocom . com.
 *
 * Licence (BSD):
 * ==============
 *
 * Copyright (c) 2004, Mikael Grev, MiG InfoCom AB. (base64 @ miginfocom . com)
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 * Redistributions of source code must retain the above copyright notice, this list
 * of conditions and the following disclaimer.
 * Redistributions in binary form must reproduce the above copyright notice, this
 * list of conditions and the following disclaimer in the documentation and/or other
 * materials provided with the distribution.
 * Neither the name of the MiG InfoCom AB nor the names of its contributors may be
 * used to endorse or promote products derived from this software without specific
 * prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
 * OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * @version 2.2
 * @author Mikael Grev
 *         Date: 2004-aug-02
 *         Time: 11:31:11
 */

abstract class Base64 {
	private static final char[] CA = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();
	private static final byte[] BA;
	private static final int[] IA = new int[256];
	static {
		Arrays.fill(IA, -1);
		for (int i = 0, iS = CA.length; i < iS; i++) {
			IA[CA[i]] = i;
		}
		IA['='] = 0;
		BA = new byte[CA.length];
		for (int i = 0; i < CA.length; i++) {
			BA[i] = (byte)CA[i];
		}
	}

	static int encodeToBytes(byte[] sArr, byte[] dArr, final int start) {
		final int sLen = sArr.length;

		final int eLen = (sLen / 3) * 3;              // Length of even 24-bits.
		final int dLen = ((sLen - 1) / 3 + 1) << 2;   // Returned character count

		// Encode even 24-bits
		for (int s = 0, d = start; s < eLen;) {
			// Copy next three bytes into lower 24 bits of int, paying attension to sign.
			int i = (sArr[s++] & 0xff) << 16 | (sArr[s++] & 0xff) << 8 | (sArr[s++] & 0xff);

			// Encode the int into four chars
			dArr[d++] = BA[(i >>> 18) & 0x3f];
			dArr[d++] = BA[(i >>> 12) & 0x3f];
			dArr[d++] = BA[(i >>> 6) & 0x3f];
			dArr[d++] = BA[i & 0x3f];
		}

		// Pad and encode last bits if source isn't even 24 bits.
		int left = sLen - eLen; // 0 - 2.
		if (left > 0) {
			// Prepare the int
			int i = ((sArr[eLen] & 0xff) << 10) | (left == 2 ? ((sArr[sLen - 1] & 0xff) << 2) : 0);

			// Set last four chars
			dArr[start + dLen - 4] = BA[i >> 12];
			dArr[start + dLen - 3] = BA[(i >>> 6) & 0x3f];
			dArr[start + dLen - 2] = left == 2 ? BA[i & 0x3f] : (byte)'=';
			dArr[start + dLen - 1] = '=';
		}

		return dLen;
	}

	static int findEnd(final byte[] sArr, final int start) {
		for (int i = start; i < sArr.length; i++)
			if (IA[sArr[i] & 0xff] < 0)
				return i;
		return sArr.length;
	}

	private final static byte[] EMPTY_ARRAY = new byte[0];

	static byte[] decodeFast(final byte[] sArr, final int start, final int end) {
		// Check special case
		int sLen = end - start;
		if (sLen == 0)
			return EMPTY_ARRAY;

		int sIx = start, eIx = end - 1;    // Start and end index after trimming.

		// Trim illegal chars from start
		while (sIx < eIx && IA[sArr[sIx] & 0xff] < 0) {
			sIx++;
		}

		// Trim illegal chars from end
		while (eIx > 0 && IA[sArr[eIx] & 0xff] < 0) {
			eIx--;
		}

		// get the padding count (=) (0, 1 or 2)
		final int pad = sArr[eIx] == '=' ? (sArr[eIx - 1] == '=' ? 2 : 1) : 0;  // Count '=' at end.
		final int cCnt = eIx - sIx + 1;   // Content count including possible separators
		final int sepCnt = sLen > 76 ? (sArr[76] == '\r' ? cCnt / 78 : 0) << 1 : 0;

		final int len = ((cCnt - sepCnt) * 6 >> 3) - pad; // The number of decoded bytes
		final byte[] dArr = new byte[len];       // Preallocate byte[] of exact length

		// Decode all but the last 0 - 2 bytes.
		int d = 0;
		for (int cc = 0, eLen = (len / 3) * 3; d < eLen;) {
			// Assemble three bytes into an int from four "valid" characters.
			int i = IA[sArr[sIx++]] << 18 | IA[sArr[sIx++]] << 12 | IA[sArr[sIx++]] << 6 | IA[sArr[sIx++]];

			// Add the bytes
			dArr[d++] = (byte) (i >> 16);
			dArr[d++] = (byte) (i >> 8);
			dArr[d++] = (byte) i;

			// If line separator, jump over it.
			if (sepCnt > 0 && ++cc == 19) {
				sIx += 2;
				cc = 0;
			}
		}

		if (d < len) {
			// Decode last 1-3 bytes (incl '=') into 1-3 bytes
			int i = 0;
			for (int j = 0; sIx <= eIx - pad; j++) {
				i |= IA[sArr[sIx++]] << (18 - j * 6);
			}

			for (int r = 16; d < len; r -= 8) {
				dArr[d++] = (byte) (i >> r);
			}
		}

		return dArr;
	}
}
